Computer systems include numerous electrical components that draw electrical current to perform their intended functions. For example, a computer's microprocessor or central processing unit (“CPU”) requires electrical current to perform many functions such as controlling the overall operations of the computer system and performing various numerical calculations. Generally, any electrical device through which electrical current flows produces heat. The amount of heat any one device generates generally is a function of the amount of current flowing through the device.
Typically, an electrical device is designed to operate correctly within a predetermined temperature range. If the temperature exceeds the predetermined range (i.e., the device becomes too hot or too cold), the device may not function correctly, thereby potentially degrading the overall performance of the computer system. Thus, many computer systems include cooling systems to regulate the temperature of their electrical components. One type of cooling system is a forced air system that relies on one or more cooling fans to blow air over the electronic components in order to cool the components.
The cubic feet per minute (“CFM”) of air that can be moved across an electric device is an important factor in how much heat can be removed from the device. Thus, the capacity of a cooling fan is a critical factor in selecting an air mover for use in a cooling application. The CFM that a cooling fan can produce is governed a number of factors including: the total area of the blades generating the airflow, the free area provided for airflow through the fan, the design of the blades, and the power generated by the electric motor.
Many axial fans used in forced air systems utilize a plurality of radial blades disposed within an annular housing, or shroud. These types of fans are commonly known as shrouded fans, muffin fans, or pancake fans. The axial depth of the housing is often just deep enough to contain the blade assembly and the motor, or motors, that power the fan. The CFM and pressure generated by a shrouded fan is generally dependent on the diameter of the blades. Therefore, as more performance is needed, the diameter of the fan increases. Thus, when utilized for cooling high density computer systems, the necessary diameter of a shrouded fan may preclude its use.
Electric ducted fans are commonly used in model airplanes to provide high thrust in small packages. Although providing relatively high flow rates and pressures, these fans are often not suitable for use in electronic cooling applications. Available electric ducted fans do not meet the longevity, reliability, power consumption, acoustic, and performance requirements of electronic cooling applications.